Catalyst for hydrohalogenation of hydrocarbons

ABSTRACT

A process for hydrohalogenating methanol with a hydrogen halide using a catalyst having an initial zone of lower activity and subsequent zones of higher activity so that coke formation and pressure drop are decreased and catalyst life is increased while overall high catalyst activity is maintained. One example of such a process uses a low surface area amorphous alumina in an initial zone and then progressively higher surface area alumina in subsequent zones.

Cross Reference to Related Application

This is a divisional of application Ser. No., 699,530 filed May 14,1991, now U.S. Pat. No. 5,109,138, which is a continuation-in-part ofco-pending application Ser. No. 529,009, filed May 24, 1990, nowabandoned.

BACKGROUND OF THE INVENTION

This invention relates to catalytic hydrohalogenation processes. Inparticular, the invention relates to the catalytic hydrohalogenation ofhydrocarbyl compounds, such as methanol, to produce hydrocarbyl halides,such as methyl chloride.

Chlorinated hydrocarbons have various utilities as industrial chemicalsand solvents. For example, methyl chloride is useful as a catalystcarrier in low temperature polymerization; as a fluid for thermometricand thermostatic equipment; as a methylating agent in organic synthesis,such as the synthesis of methylcellulose; in the preparation of siliconerubbers; and as an extractant and low temperature solvent.

Methods for the production of halogenated, especially chlorinated,hydrocarbons, such as methyl chloride, are well-known. In a typicalmethod for the production of methyl chloride, vaporized methanol andhydrogen chloride are mixed in approximately equimolar proportions andpassed through a converter packed with a catalyst such as alumina gel orzinc chloride on activated carbon to form methyl chloride. Other knownmethods involve reactions in the liquid phase using an aqueous solutionof catalyst. For example, U.S. Pat. No. 4,073,816 teaches thatmonochloroalkanes or monochlorocycloalkanes can be prepared by reactingan alcohol with hydrogen chloride in the presence of aqueous zincchloride. German Offentlegungschrift 3332253 teaches that mixturescontaining alcohols and ethers may be converted to alkyl halides byreactions with hydrogen chloride in the gas phase in the presence of anzinc chloride on aluminum oxide catalyst. This reference further teachesthat small amounts of alkali metal chlorides and larger amounts ofcadmium, iron and/or magnesium chlorides may be added with the zincchloride to increase the efficiency of the catalyst.

Such methods do not resolve all the existing problems relating to themanufacture of chlorinated hydrocarbons. The problems include excessiveproduction of byproducts; requirements for use of excess hydrochloricacid and excessive coking of the catalyst. An additional problem relatedto the use of alumina or alumina supported catalysts is the chemicalbreakdown of the alumina to produce other less desirable types ofalumina such as boehmite, a monohydrate of alpha-alumina, and alsophysical attrition. What is needed is a catalyst which results in a highyield of chlorinated hydrocarbyl compound which also permits thecomplete conversion of hydrochloric acid; which does not experienceexcessive coke formation; which reduces the amount of byproducts formed;which decreases the formation of boehmite; and which is more resistantto attrition.

SUMMARY OF THE INVENTION

This invention comprises a vapor process for hydrohalogenating methanolwith a hydrogen halide wherein a hydrohalogenation catalyst having atleast two zones is used, wherein the first zone contains catalyst havinglower activity and subsequent zones contain catalyst havingprogressively higher activity.

The process and catalyst provided by the present invention have beenshown to decrease coke formation by lowering the peak reactiontemperature, or reaction hot spot, while still providing high overallconversion to product. The decrease in the reaction hot spot inconjunction with successively more active catalyst zones have severalbenefits among which are increased production, decreased by-productformation and increased catalyst life.

DETAILED DESCRIPTION OF THE INVENTION

The process of vapor phase hydrohalogenation is often terminated becauseof high pressure drop in the reactor or low catalytic activity. Highpressure drop results from coke formation on and around the catalystwhich decreases space for gas flow. When an alumina catalyst is used,fracturing and powdering of the alumina catalyst also causes plugging.Loss of catalytic activity results from sintering and coke formation ingeneral and additionally from boehmite formation when alumina catalystsare used.

The majority of coke formation in hydrohalogenation reactors istypically located in the initial zone of the catalyst bed where thetemperature peaks. This also known as the reactor hot spot. The hot spothas also been found to be the site where most catalyst sintering occursand where the catalyst loses activity first and to the greatest degree.

The use of a catalyst having a lower activity in an initial contact zonereduces the hot spot in the hydrohalogenation reactor catalyst bed andthus reduces the formation of coke and increases catalyst life. It hassurprisingly been found that the use of the low activity zone incombination with one or more subsequent zones having progressivelyincreasing activity maintains or improves overall conversion and yieldwhile still obtaining the benefits of lowering the reaction hot spot.

Control of catalyst activity is accomplished by (1) controlling catalystsurface area when using alumina itself as a catalyst and/or (2)controlling the catalyst concentration in a supported catalyst system.

One aspect of this invention is exemplified by the use of an amorphousalumina catalyst to hydrohalogenate methanol with hydrogen chloride. Inthis process the catalyst bed has multiple zones wherein the first zonehas alumina having a surface area of from about 20 to about 100 m² /gand subsequent zones have increasingly larger surface areas, e.g., for atwo zone arrangement the second zone has a catalyst having a surfacearea of greater than about 100 m² /g. The total number of zones in thecatalyst bed is at least two. The upper limit on the number of zones isprimarily determined by the ability to mechanically construct the bed.Based on practical considerations, it is preferred that the catalyst bedhave no more than ten zones, more preferably no more than six zones. Itis most preferred that the catalyst bed have from two to four zones.

Practically speaking, most alumina hydrohalogenation catalysts haverelatively high surface area. Such catalysts typically have a surfacearea greater than about 320 m² /g and such amorphous alumina catalystsare highly active.

In accord with a preferred embodiment of the present invention however,the reactor hot spot temperature is lowered and the reaction spread overa greater portion of the catalytic bed by using an amorphous alumina ina first zone comprising 10 to about 50 percent, and most preferably fromabout 10 to about 30 percent, and most preferably from about 15 to about25 percent of the catalytic bed. This initial contact catalyst zonecomprises amorphous alumina having a surface area of 100 m² /g or less,preferably from about 40 to about 100 m² /g and more preferably fromabout 40 to about 70 m² /g. A secondary zone of the catalytic bed in thehydrohalogenation reactor comprises from about 10 to about 50 percent,preferably from about 10 to about 30 percent, most preferably from about15 to about 25 percent of the catalyst. This medium zone has amorphousalumina which has a surface area of from about 50 to about 150 m² /g,more preferably from about 70 to about 150 m² /g, and most preferablyfrom about 80 to 130 m² /g. The remaining zone of the catalytic bed inthe hydrohalogenation reactor comprises from about 0 to about 80percent, more preferably from about 40 to about 80 percent and mostpreferably from about 50 to about 70 percent of the reactor. This zoneof the catalyst comprises amorphous alumina having a surface areagreater than about 150 m² /g, especially from about 150 to about 320 m²/g, more preferably from about 150 to about 250 m² /g and mostpreferably from about 150 to about 220 m² /g. It should be noted that,while the ranges of catalyst surface areas given for the variouscatalyst zones overlap, selection of the surface area used in each casewill be selected to result in each zone having different, progressivelyhigher catalyst surface areas. It should also be noted that while apreferred embodiment showing three zones is set forth, other catalystsystems may comprise two, four or more beds having similar arrangements.

While such amorphous alumina materials may not be novel per se, andwhile some small portions of such amorphous aluminas may be found inother hydrohalogenation processes or literature references, it has notheretofore been known to combine relatively low surface area alumina inan initial contact zone with additional zones having progressivelyhigher surface areas and wherein the high surface area has a limitedrange surface area to produce a catalytic bed which evidences a lowerreactor hot spot temperature, increased catalyst life and decreasedalumina phase transformation, decreased particle attrition and decreasedcoke forming tendencies while maintaining high overall conversion andyield. These advantages result in increased productivity, lowerproduction costs and longer catalyst life.

A reduction in the surface area of amorphous alumina is an easilyobtained result and is not a part of this invention. Further,preparation of a low surface area alumina is documented in theliterature. In order to prepare alumina from crude aluminum hydroxide,one treatment is to calcine the material at 600°-800° C. until thesurface area desired is obtained. High surface area aluminas, havinggreater than about 200 m² /g, can be readily obtained commercially. Itis then only necessary to heat the alumina for a time sufficient toreduce the surface area, cool it and determine the resultant loweredsurface area by conventional procedures. If the desired surface area hasnot been reached, the heating step is repeated until the desired surfacearea is obtained.

Any amorphous alumina can be employed in the present invention. However,beta, gamma, eta, chi and similar amorphous aluminas are typicallyemployed. The hydrated form of alumina, namely boehmite, produced by theaction of water at lower temperatures in the hydrohalogenation process,is to be avoided because it is less efficient. Preferably, gamma aluminais employed as the catalyst in the present invention.

The alumina catalyst is not limited to any particular shape or size.Known and useful shapes include granules, flakes, spheres, tables,powder and extruded shapes such as rings, cylinders and lobes. Also thesize of the catalyst employed is typically from about 1/8 inch 6.32 cm)to about 1/2 inch (1.27 cm). The shape and size of conventionalcatalysts used in hydrohalogenation reactions are useful in the presentinvention, being careful to follow general good engineering principles.For example, in a packed bed, the pressure drop across a bed of rings orlobed shapes is less than that of a sphere or extrudate shape of similardimensions.

In a second embodiment of the present invention, it has been found thatwhen the hydrohalogenation catalyst used is a supported catalyst, theuse of different catalyst concentration levels and, optionally differentsupports, results in control of the catalyst activity. Catalyst activityis controlled by using different catalyst concentrations in the variouszones of the catalyst with lowest concentration in the first zone andprogressively greater concentration in the subsequent zone or zones. Asis obvious, the subsequent zone or zones of the catalyst is that portionof the catalyst where secondary or subsequent contact occurs.

The supported catalyst useful in this embodiment of the presentinvention is advantageously a salt of a Group IA metal (alkali metal); aGroup IIA or IIB, preferably Group IIB, metal; and a neutralizing numberof counter anions supported on a non-alumina porous carrier material.Preferred Group IA metals include sodium, potassium, rubidium, lithiumand cesium, with potassium and cesium being more preferred and potassiumbeing most preferred. The preferred Group IIB metals include zinc,cadmium and mercury with zinc being more preferred. While any counteranion, such as bromide, chloride and fluoride, is suitable in thecatalyst of this invention, the halides are preferred with chloridebeing most preferred. Other suitable anions are nitrates, sulfate,phosphate, acetates, oxylate and cyanides. Thus, a most preferredsupported catalyst is a zinc chloride/potassium chloride catalyst.

The molar ratio of Group IA metal to Group IIA or IIB metal in the saltis preferably at least about 0.5:1 and no greater than about 1.5:1. Itis more preferred that the molar ratio is at least about 0.9:1 and nogreater than about 1.1:1 and most preferred that approximately equimolarportions of the two metals are used. The amount of counter anion used isthat which is sufficient to neutralize the cations of the salt.

Any support which will withstand the hydrochlorination conditionsdescribed herein can be used in the process of the present invention.Examples of appropriate supports include the well-known carbon supportssuch as activated carbon, carbon black, chars and coke. Alumina supportsare also appropriate. Any amorphous alumina can be employed in thepresent invention. However, beta, gamma, eta, chi and similar amorphousaluminas are typically employed. The hydrated form of alumina, namelyboehmite, produced by the action of water at lower temperatures in thehydrohalogenation process, is to be avoided because it is lessefficient. Preferably, gamma alumina is employed as the catalyst supportin the present invention. In particular, alumina supports having asurface area from about 25 m² /g to about 320 m² /g are preferred, withsurface areas from about 40 to about 200 m² /g being more preferred. Itis also preferred that alumina supports are designed such that thepercent surface area and pore volume in the pore diameters below 50angstroms, more preferably 100 angstroms, is minimized so that thealumina support has a minimum pore size distribution in the area of 100angstroms or less. Other suitable supports that may be used to supportthe catalyst include pumice, silica gel, asbestos, diatomaceous earth,fullers earth, titania, zirconia, magnesia, magnesium silicate, siliconcarbide, silicalite, and silica. Of this latter group, a preferredsupport is silica. A silica having a surface area between 100 m² /g and300 m² /g and a pore volume in the range of 0.75 cc/g to 1.4 cc/g isparticularly suitable.

In a preferred embodiment, the supported catalyst used is a zincchloride/potassium chloride catalyst. Practically speaking, zincchloride/potassium chloride catalysts have significant activity for theconversion of alcohols such as methanol to organic halides such asmethyl chloride. In accord with the present invention however, thereactor hot spot temperature is lowered and the reaction spread over agreater portion of the catalytic bed by the practice of this invention.This is accomplished by using a supported ZnCl₂ /KCl catalyst having aspecified lower concentration over the first about 10 to about 50percent of the catalytic bed in an initial contact zone of thehydrohalogenation reactor. The subsequent zone or zones of the catalystcomprise from about 90 to about 50 percent of the catalytic bed whereinsubsequent contact occurs. As discussed above in connection with theamorphous aluminum catalyst, the subsequent zone may be a single zone ormay itself be divided into two or more zones. This subsequent zone orzones of the catalyst utilizes a supported ZnCl₂ /KCl catalyst which hasprogressively higher catalyst concentration than the first zone of thecatalyst. The use of such a catalyst system, having at least two zonesresults in a lower reactor hot spot temperature, increased catalyst lifeand decreased coke forming tendencies. These advantages result inincreased productivity, lower production costs and longer catalyst life.

It is preferred that the concentration of the catalyst in the first zoneof the catalyst bed is at least about one percent and no greater thanabout ten percent. The concentration in the second zone is preferably atleast about five percent and no greater than about fifty percent. Whenmore than two catalyst zones are used, the catalyst concentration ineach subsequent zone increases over the preceding zone.

The catalyst system useful in the practice of this invention is notlimited to any particular shape or size. Known and useful shapes includegranules, flakes, spheres, tables, powder and extruded shapes such asrings, cylinders and lobes. Also the size of the catalyst employed istypically from about 1/8 inch (0.32 cm) to about 1/2 inch (1.27 cm). Theshape and size of conventional catalysts used in hydrohalogenationreactions are useful in the present invention, being careful to followgeneral good engineering principles. For example, in a packed bed, thepressure drop across a bed of rings or lobed shapes is less than that ofa sphere or extrudate shape of similar dimensions.

The salts are suitably supported on the carrier material by any standardimpregnation technique such as that disclosed in Experimental Methods inCatalytic Research, Vol. II, edited by R. B. Anderson and P. T. Dawson,Academic Press, New York, 1978. A solution of both the Group IA andGroup IIA or IIB metal cations and the associated anions may be employedto impregnate the support material or the metal salts may be impregnatedfrom separate solutions. The resulting catalyst comprising thecatalytically active salt and the support preferably comprises fromabout 1 to about 50 weight percent of the Group IIA or IIB metal salt,e.g., ZnCl₂, and from about 0.5 to about 30 weight percent of the GroupIA metal salt, e.g., KCl, based on the percentage by weight of the totalsalts to the support. It is preferred to use at least about 20 and nogreater than about 30 weight percent of the Group IIA or IIB metal saltand at least about 10 and no greater than about 20 weight percent of theGroup IA metal salt and more preferred to use about 20 weight percent ofthe Group IIA or IIB metal salt and about 10 weight percent of the GroupIIA metal salt. Preferred weight percents of the two salts are selectedso as to result in approximately equimolar proportions of the Group IAand Group IIA or IIB salt being used.

The initial low activity zone of the catalyst and subsequent zones ofincreasing activity may be obtained by any combination of the catalystzones described above. For example, a catalyst system of the presentinvention may comprise an initial zone of low surface area alumina,medium zone or zones of increasingly higher surface area alumina and afinal very high activity zone of a supported catalyst on alumina. Aparticular benefit of the present invention is that zones of very highactivity may be used in conjunction with the lower activity initial zoneto result in a catalyst with very high overall activity in combinationwith long life.

The process of the present invention comprises contacting a loweralkanol such as methanol, ethanol or propanol and hydrogen chloride inthe presence of the aforementioned catalyst systems under reactionconditions sufficient to produce the corresponding chlorinatedhydrocarbon. It is preferred that the alkanol is methanol.

Molar ratios of lower alkanol to hydrogen halide, preferably hydrogenchloride, useful in the practice of this invention are generally atleast about 1:10 and no greater than about 10:1. It is preferred thatthe molar ratio is from 1:5 to 5:1, more preferably 1:1.5 to 1.5:1. Itis most preferred that the molar ratio approach stoichiometric, that isfrom 1:1.25 to 1.25:1.

The temperature range useful in the practice of this invention is any atwhich the hydrochlorination reaction will proceed. Preferably, thereaction is conducted at a temperature of at least about 25° C. and nogreater than about 475° C. with at least about 175° C. to no greaterthan about 300° C. being more preferred. The most preferred temperatureranges from at least about 220° C. to no greater than about 280° C.Pressures typically employed in the process of the present invention areat least about atmospheric and no greater than about 500 psig. Preferredpressures are at least about 35 psig and no greater than about 150 psig.

Gas hourly space velocities (number of reactor volumes processed instated time period) are suitably at least about 100 and no greater thanabout 10,000 hours⁻¹, preferably at least about 300 and no greater thanabout 3000 hr⁻¹.

The process may be operated in a batch mode or continuously althoughcontinuous operation is preferred. In a preferred embodiment, vaporizedmethanol and hydrogen chloride are added in approximately equimolarproportions to a fixed bed reactor containing the zoned catalyst of thepresent invention. The resultant products are separated by conventionalmeans.

The present invention may comprise, consist essentially of or consist ofthe process described above and may be practiced in the absence of anystep or element not specifically described.

The following examples are provided to illustrate the invention andshould not be interpreted as limiting the invention in any manner.Unless otherwise indicated, all parts and percentages are by weight. Theexperimental data obtained are in connection with a hydrochlorinationreaction carried out in a 20 foot (6.1 meter) vertical 11/4 inch (3.18cm) diameter Inconel tube into which is placed the alumina catalyst asdescribed in each experiment. The gaseous methanol and hydrogen chlorideare fed to an insulated double pipe heat exchanger and heated toreaction temperature with a suitable heat transfer medium, such as ablend of about 40 percent diphenyl oxide and about 60 percent biphenylylphenyl ether. Thermocouples are attached at intervals along the reactortube length to measure the temperature at various depths in the catalystbed. After mixing and heating in the double pipe heat exchanger thegaseous mixture is introduced into the top of the hydrochlorinationreactor and passes through the catalyst, exiting as product methylchloride, byproducts, unreacted feed gases and water vapor. The effluentgaseous mixture can be condensed by a suitable heat exchanger andseparated to recover pure product and recycle feed gases.

EXAMPLE 1

The general reaction scheme described above was used. The initial 4 feet(1.22 meters) of the reactor was loaded with 60 m² /g alumina and theremaining section of the reactor was filled with 200 m² /g alumina. Theflow rate for methanol was 3.94 lb/hr (1.79 kg/hr) and for hydrogenchloride was 5.3 lb/hr (2.41 kg/hr) at 50 psig. A reaction using asingle catalyst zone with 200 m² /g alumina was also run. Thetemperature profiles for these systems at 240° C. heat transfer fluidtemperatures are shown in Table I. Additionally, the table shows themethanol conversion and the amount of dimethyl ether (DME) producedrelative to methyl chloride (M1). With this stratified catalyst systemthere is only a small broad hot spot instead of the typical large,narrow hot spot observed when the reactor is loaded with only aluminawith surface area greater than 200 m² /g.

                  TABLE I                                                         ______________________________________                                        REACTOR      BULK GAS TEMPERATURE, °C.                                 DEPTH,       200 m.sup.2 /g                                                                            60 + 200 m.sup.2 /g                                  ft.          ALUMINA     ALUMINA                                              ______________________________________                                        1            370         256                                                  2            272         265                                                  4            241         252                                                  6            239         246                                                  9            239         242                                                  12           239         241                                                  Methanol conv                                                                              99.7%       99.4%                                                DME/M1 ratio 1591 ppm    4967 ppm                                             ______________________________________                                    

In a preferred embodiment wherein methanol and hydrogen chloride reactto form methyl chloride, the process of the present invention utilizingan amorphous alumina catalyst system results in a long-lived catalyst.This catalyst is stable and the decreased temperature of the reactor hotspot decreases coke formation and pressure drop. Further, the increasein average pore size decreases the conversion of amorphous alumina toboehmite.

EXAMPLE 2

The reactor described above is loaded as follows:

Fourteen weight percent KCl supported on silica is loaded into the firstfoot (0.3 m) of the reactor

Next 4.5 (1.4 m) feet is loaded with ZnCl₂ /KCl supported on silica with5 weight percent ZnCl₂ and a 1.1:1 molar ratio of KCl to ZnCl₂

Next 10 (3.04 m) feet is loaded with ZnCl₂ /KCl supported on silica with17.5 weight percent ZnCl₂ and a 1.0:1 molar ratio of KCl to ZnCl₂

The catalyst is dried overnight at 220° C. in nitrogen and conditionedfor 15 minutes with HCl at 220° C.

In the gas phase using the above reactor scheme and general procedure,the proportions of methanol to hydrogen chloride and the reactiontemperature are varied as shown in Table II below. The reactor effluentis analyzed by gas chromatography to determine the conversion obtainedand the amount of dimethyl ether produced relative to the amount ofmethyl chloride produced. The results obtained are shown in Table IIbelow. In Runs 1 and 2, a temperature profile is determined by measuringthe temperature at various reactor depths as shown in Table III below.

                  TABLE II                                                        ______________________________________                                                                              HCl                                                   HCl    Exc        Meth. Con-   DME/                                  Methanol (lb/   HCl  Temp  Conv  version.sup.1                                                                        MC.sup.2                         Run  (lb/hr)  hr)    (%)  (°C.)                                                                        (%)   (%)    (ppm)                            ______________________________________                                        1    8.00     10.00  10   220   94.2  87.1  7076                              2    8.00     10.00  10   235   95.4  88.8  5930                              3    3.92     5.57   25   220   99.1  83.9  2761                              4    3.92     5.57   25   220   99.2  --    2097                              5    3.92     4.91   10   220   98.0  89.1  4349                              6    7.46     10.57  25   220   97.5  78.7  3598                              7    5.83     7.78   17   220   97.6  84.0  4083                              8    4.14     4.95   5    220   97.2  90.5  5620                              9    4.24     4.84   0.3  220   96.9  92.1  5944                              10   3.29     4.12   10   220   98.6  87.5  3494                              11   3.29     3.67   -2   220   96.8  93.9  6869                              12   10.51    14.95  25   220   96.0  78.1  4341                              13   10.51    11.72  -2   220   89.9  88.8  8363                              ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        REACTOR          BULK GAS                                                     DEPTH,           TEMPERATURE, °C.                                      ft.              220° C.                                                                        235° C.                                       ______________________________________                                        1                243     252                                                  2                242     254                                                  4                238     250                                                  6                259     269                                                  9                228     238                                                  ______________________________________                                    

The data in Table II above shows the effectiveness of the presentinvention utilizing a supported zinc chloride/potassium chloridecatalyst in obtaining high methanol conversion and good selectivity. Theratio of dimethyl ether (DME) to methyl chloride is given in the lastcolumn and shows the parts of DME produced per million parts of methylchloride.

The data in Table III above shows that the reaction has been delocalizedresulting in a moderation of any hot spots. This is accomplished withoutsignificant detrimental impact on methanol conversion or dimethyl etherby-product production.

EXAMPLE 3

A production scale reactor constructed of Iconel 600 consisting of 1,532tubes, each having a diameter of 1.25 feet (0.38 m) and a length of 16feet (4.9 m) is loaded with commercial grade 150 m² /g alumina andoperated for a period of 126 days. To test the effect of alumina surfacearea on carbon formation, three individual tubes of the reactor areloaded with aluminas of surface areas of 125, 105 and 50 m² /grespectively, as shown in Table IV below. An analysis of the carboncontent of the three test tubes along the depth of the reactor at theend of the 126 days run is given in Table IV below.

                  TABLE IV                                                        ______________________________________                                        REACTOR    CARBON CONTENT, (WT PERCENT)                                       DEPTH,     125 m.sup.2 /g                                                                            125 m.sup.2 /g                                                                         125 m.sup.2 /g                                ft.        Alumina     Alumina  Alumina                                       ______________________________________                                        3          19.41       13.78    8.44                                          4          12.76       6.37     3.91                                          5          8.47        1.35     0.78                                          6          3.90        0.44     0.16                                          ______________________________________                                    

The data shown above demonstrates that lower surface area aluminasmoderate the amount of decomposition which occurs, leading to productdecomposition.

What is claimed is:
 1. A hydrohalogenation catalyst having reducedcoking, decreased pressure drop over the catalyst lifetime, andincreased catalyst life in a hydrohalogenation reactor charge for thereaction of methanol and a hydrogen halide gas mixture, said catalystcomprising at least two zones wherein the catalytic activity forhydrohalogenation of each zone is lower than that of each succeedingzone.
 2. The catalyst of claim 1, wherein said hydrohalogenationcatalyst is an alumina selected from the group consistency of beta,gamma, eta and chi alumina and initially free from boehmite.
 3. Thecatalyst of claim 2 wherein said hydrohalogenation catalyst has aminimum pore size distribution in the area of 100 Å or less.
 4. Thecatalyst of claim 1 comprising a first zone wherein the catalyst isselected from a lower surface area alumina of from about 20 to about 100m² /g of surface area and a second zone wherein the catalyst is selectedfrom surface area alumina of from about 50 to about 150 m² /g and athird zone wherein the catalyst is selected from alumina having greaterthan about 150 m² /g of surface area, in which said catalyst bed hassaid first zone contacting said hydrocarbyl alcohol and said hydrogenhalide gas mixture initially with the remaining catalyst zones havingsaid higher surface area alumina catalyst, with the proviso that eachsucceeding zone have alumina with surface area higher than in thepreceding zone.
 5. The catalyst of claim 1 comprising a first zonewherein the catalyst is selected from a lower surface area alumina offrom about 20 to about 100 m² /g of surface area and a second zonewherein the catalyst is selected from surface area alumina havinggreater than about 100 m² /g of surface area, in which said catalyst bedhas said first zone contacting said hydrocarbyl alcohol and saidhydrogen halide gas mixture initially with the remaining catalyst zonehaving said higher surface area alumina catalyst, with the proviso thateach succeeding zone have alumina with surface area higher than in thepreceding zone.